If the meta is going to be full of dive comps like people predict and with the Ana nerf, expect to see a lot more Mercy.

I don't think this issue is as one sided as people make it out to be. The pro players know how to improve the game and make it more competitive, but Blizzard know how to make Overwatch attractive to a larger audience and making the game grow.

A compromise between the sides is crucial, there can't be maps which are played 10x as frequently as others.

I suggest splitting the maps into groups based on how much they are played. For example, in a BO3 they can be split in 3 groups, with the 4-5 most popular being played 1st, next 4-5 played 2nd etc with some form of pick/ban. Players would be able to choose which maps they play, and less popular maps would be player (albeit not all the time). This would no doubt be imperfect, however it's just a suggestion and can definitely be refined.